Polyphenols and high-performance resins from syringaldehyde

ABSTRACT

A method to generate renewable high performance composites and thermoplastics. These materials can be generated from a renewable phenol (syringaldehyde) that can be derived from lignocellulosic biomass. The use of syringaldehyde as a precursor to composites has the potential to reduce the cost and environmental impact of structural materials, while meeting or exceeding the performance of current petroleum derived resins.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation non-provisional patent application, claiming thebenefit of, parent application Ser. No. 14/172,701 filed on Apr. 20,2015 which claims benefit to provisional application Ser. No. 61/769,297filed on Feb. 26, 2013, and is co-pending with patent application Ser.No. 14/172,673 filed on Feb. 4, 2014 which also claims benefit toprovisional application Ser. No. 61/769,297 filed on Feb. 26, 2013,whereby the entire disclosure of which is incorporated hereby reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

The invention described herein may be manufactured and used by or forthe government of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

FIELD OF THE INVENTION

The invention generally relates to methods to efficiently generatepolyphenols, thermoplastics, and high temperature resins/thermosets fromsyringaldehyde. High value phenolic compounds includingtrans-resveratrol can be generated by this approach.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a flow chart showing methods to efficiently generatepolyphenols, thermoplastics, and high temperature resins/thermosets fromsyringaldehyde, according to embodiments of the invention.

It is to be understood that the foregoing general description and thefollowing detailed description are exemplary and explanatory only andare not to be viewed as being restrictive of the invention, as claimed.Further advantages of this invention will be apparent after a review ofthe following detailed description of the disclosed embodiments, whichare illustrated schematically in the accompanying drawings and in theappended claims.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The invention generally relates to methods to generate renewable highperformance composites and thermoplastics. These materials can begenerated from a renewable phenol (syringaldehyde) that can be derivedfrom lignocellulosic biomass. The use of syringaldehyde as a precursorto composites has the potential to reduce the cost and environmentalimpact of structural materials, while meeting or exceeding theperformance of current petroleum derived resins.

Bisphenol compounds such as BPA (bisphenol A) are widely used asbuilding blocks for a variety of commercial and industrial products.Specifically, bisphenols are the building blocks for polycarbonateplastics, epoxy resins, polyester resins, cyanate ester resins and otherpolymers/resins which include but are not limited to polycarbonates,polysulfones, polyesters, polyester-styrene, alkylphenolics, andpolyalylates. Commercially available bisphenol compounds, especiallypolyaromatic bisphenols, are currently derived from petroleum.

In an effort to create more sustainable bisphenol building blocks wehave developed a series of polyaromatic bisphenol compounds derived fromsyringaldehyde. Syringaldehyde can be isolated from crude biomassfeedstocks that include lignin and the current invention describes amethod to efficiently convert syringaldehyde into polyphenols. Theability to either homocouple syringaldehyde or cross-couplesyringaldehyde with various renewable aldehydes allows for the synthesisof a variety of trifunctional and tetrafunctional bisphenols that can beconverted to resins with exceptional glass transition temperatures. Theutilization of renewable polyphenols as precursors to epoxies,polycarbonates, and high temperature thermosets including cyanateesters, provides an opportunity to develop full-performance resins whilereducing the use of petroleum based feedstocks. This approach will thendiminish the overall environmental impact of resin production whileallowing for a sustainable source of phenols.

Some references in the literature include: CN 1736986 A describes thesynthesis of 3,3′-5,5′-tetramethoxystilbene via a Wittig reaction; U.S.Pat. No. 4,087,336 describes electrochemical reduction of variousp-benzaldehydes to stilbenes; and Dieguez, H. R. et al. J. Am. Chem.Soc. 2010, 132, 254-259 describes the synthesis of3,3′-5,5′tetramethoxystilbene via Cp₂TiCl mediated reductive coupling.

FIG. 1. is a flow chart showing methods to efficiently generatepolyphenols, thermoplastics, and high temperature resins/thermosets fromsyringaldehyde.

1. Syringaldehyde is isolated from a renewable source (lignin). Thisstep can include oxidation of lignin with oxygen, peroxides, or aromaticnitro-compounds among others. The oxidation step can be conducted withor without a transition metal catalyst. Syringaldehyde can also berecovered from the black liquor resulting from the Kraft pulpingprocess.

2A. Syringaldehyde is directly coupled to a renewable aldehyde throughchemical or electrochemical means. This step can be conducted via atransition metal mediated McMurry coupling or by applying a potential ina standard electrochemical setup to reductively couple the aldehydes.

3A. The reductively coupled product is converted to a polyphenolprecursor by the following steps:

3Ai. Reductive coupling products generated by a McMurry reaction arehydrogenated to generate a saturated coupling product.

3Aii. The vicinal diols of reductive coupling products generatedelectrochemically are either reduced by hydrogenation or are protectedand then reductively eliminated

3Aiii. Saturated coupling products are then converted to polyphenolprecursors by dehydrodeoxygenation which is accomplished via conversionof phenols to sulfonates and subsequent reductive elimination withtransition metal catalysts.

Alternate method for generation of polyphenol precursors:

2B. Syringaldehyde is converted to a reductive coupling product by:

2Bi. conversion to a sulfonate followed by reductive elimination togenerate 3,5-dimethoxybenzaldehyde.

2Bii. 3,5-dimethoxybenzaldehyde is reductively coupled either by atransition metal mediated McMurry reaction or electrochemically to yielda reductive coupling product.

3B. Reductive coupling products are converted to polyphenol precursorsby the following steps:

3Bi. Reductive coupling products generated by a McMurry reaction arehydrogenated to directly yield a polyphenol precursor

3Bii. The vicinal diols of electrochemically generated reductivecoupling products are either reduced by hydrogenation or are protectedand then undergo reductive elimination to generate a polyphenolprecursor.

4. Polyphenol precursors are converted to polyphenols by a demethylationreaction. Reagents for this step may include BBr₃ or pyridiniumhydrochloride.

5. Polyphenols are converted to thermoplastics by methods known in theart.

6. Alternatively, polyphenols can be converted to resins includingcyanate ester and epoxy resins.

7. Resins can be blended with support materials including glass orcarbon fibers and thermally cured with or without a catalyst to generatea composite material.

The McMurry reaction is an organic chemical reaction under which twoketone or aldehyde groups combine to form an alkene in the presence of atitanium species resulting from reduction of a titanium (III or IV)compound with a reducing metal such as magnesium or zinc. The reactionmay occur by a free radical process, similar to that observed in thepinacol coupling of aldehydes and ketones in the presence of a reducingmetal, followed by an elimination of oxo-titanium species, owing to thestrong bond that oxygen and titanium share. In some cases McMurryreactions can be catalytic with respect to titanium when stoichiometricchlorinating agents such as alkyl silyl chlorides are added to thereaction mixture. Other transition metal compounds based on tungsten arealso effective at mediating McMurry reactions. The electrochemicalcoupling can be achieved by applying the appropriate voltage to a saltsolution including the two ketones or aldehydes including compounds toform a coupled diol product. The reaction is run using a standard threeelectrode setup where the working and auxillary electrodes are selectedfrom lead, platinum, mercury, nickel, gold, or carbon; and performed atany voltage at which hydrogen evolution occurs at the chosen electrode.After the reaction the product diol is precipitated from the saltsolution by acidification.

Syringaldehyde can be isolated from lignin or lignocellulosic feedstocksby chemical or enzymatic oxidation. It can also be prepared from otherlignin decomposition products including vanillin. There are severalmethods available to couple syringaldehyde to other aldehydes. A directchemical method including McMurry coupling can be utilized to combinethe two aldehydes with generation of a double bond. Alternatively, anelectrochemical method can be utilized to generate a diol. The diol canthen be chemically reduced by various methods including hydrogenation orprotection/deprotection through either chemical or electrochemicalmethods. In embodiments, the diol can be converted to a diacetate oroxalate and then reduced to the olefin electrochemically. When a mixtureof aldehydes is utilized, a distribution of homocoupling andcross-coupling products will result. In some cases, the distribution canbe controlled by the reactivity of a given aldehyde. The distributioncan also in some cases be controlled by solubility. Mixtures of coupledproducts can be used directly or purified through various meansincluding crystallization, column chromatography, distillation, andsublimation. Dehydrodeoxygenation can be accomplished by conversion ofthe phenol to a sulfonate (e.g. mesylate, tosylate, triflate). Reactionwith zero valent nickel or palladium then results in reductiveelimination. Both heterogeneous and homogenous catalysts are suitablefor the reductive elimination. The methoxy groups can be converted tohydroxy groups by a variety of methods including reaction with borontribromide (BBr₃) or pyridinium hydrochloride. Dehydrodeoxygenation isconducted as in steps described above. The resulting aldehyde is coupledas described above. In the case of electrochemical coupling of moleculeswith limited solubility in water, a non-aqueous solvent with a broadelectrochemical window, including acetonitrile, is used and anadditional hydrogen source must be introduced. Various resins can beprepared from the polyphenols by techniques known in the art. Inembodiments, the polyphenols can be converted to cyanate esters byreaction with a suitable base and a cyanogen halide. Polyphenols canalso be converted to epoxy resins by reaction with epichlorohydrin.Various thermoplastics can be prepared from the polyphenols bytechniques known in the art. In embodiments, the polyphenols can beconverted to polycarbonates by reaction with reagents includingphosgene, triphosgene, and diphenylcarbonate. In other embodiments,thermoplastics including polysulfones, polyesters, polyester-styrenepolymers, alkylphenolics, and polyalylates can be prepared from thepolyphenols. Composites can be fabricated by combining resins orthermoplastics with various fibers (including carbon or glass fibers)and curing the composites through either thermal or chemical means.

In other embodiments, please see the schematics and reaction schemesherein. Scheme 1 illustrates the process by which syringaldehyde isfirst deoxygenated to 3,5-dimethoxybenzaldehyde in two steps. The phenolis converted to a mesylate, tosylate, or triflate. Then reductiveelimination is achieved by reaction with zero valent nickel or palladiumto produce the benzaldehyde. The 3,5-dimethoxybenzaldehyde is then usedin the McMurry coupling reaction either alone or with another aldehydeor ketone to produce either the homo-coupled or hetero-coupled product,respectively. The coupled product is then hydrogenated under standardconditions with Pt, Pd, or Ni under ˜40 psi of hydrogen. The saturatedproduct is then demethylated using a catalyst including pyridiniumhydrochloride or boron tribromide to give the polyphenol. The polyphenolis then reacted with cyanogen bromide or a similar cyanogen halide orpseudohalide and a base including triethylamine to yield the cyanateester.

Scheme 2 illustrates the process by which syringaldehyde is firstdeoxygenated to 3,5-dimethoxybenzaldehyde in two steps. The phenol isconverted to a mesylate, tosylate, or triflate. Then reductiveelimination is achieved by reaction with zero valent nickel or palladiumto produce the benzaldehyde. The 3,5-dimethoxybenzaldehyde is then usedin an electrochemical coupling reaction either alone or with anotheraldehyde or ketone to produce either the homo-coupled or hetero-coupleddiol product, respectively. The coupled product is then reduced eitherthrough hydrogenation, or protection and reductive elimination(chemically or electrochemically) to produce a polyphenol precursor. Thepolyphenol precursor is then demethylated using a catalyst includingpyridinium hydrochloride or boron tribromide to give the polyphenol. Thepolyphenol is then reacted with cyanogen bromide or a similar cyanogenhalide or pseudohalide and a base including triethylamine to yield thecyanate ester.

Scheme 3 illustrates the process by which syringaldehyde is first usedin the McMurry coupling reaction either alone or with another aldehydeor ketone to produce either the homo-coupled or hetero-coupled product,respectively. The coupled product is then hydrogenated under standardconditions with Pt, Pd, or Ni under ˜40 psi of hydrogen. The coupledproducts are then deoxygenated in two steps. Deoxygenation takes placeby converting the phenol to a sulfonate (e.g. mesylate, tosylate, ortriflate). Then reductive elimination is achieved by reaction with zerovalent nickel or palladium to produce the polyphenol precursor. Thedeoxygenated product is then demethylated using a catalyst includingpyridinium hydrochloride or boron tribromide to give the polyphenol. Thepolyphenol is then reacted with cyanogen bromide or a similar cyanogenhalide or pseudohalide and a base including triethylamine to yield thecyanate ester.

Scheme 4 illustrates the process by which syringaldehyde is used in theelectrochemical coupling reaction either alone or with another aldehydeor ketone to produce either the homo-coupled or hetero-coupled diolproduct, respectively. The coupled dial product is then reduced eitherthrough hydrogenation or protection and reductive elimination(chemically or electrochemically) to produce the saturated product. Thecoupled product is then deoxygenated in two steps. Deoxygenation takesplace by converting the phenol to a sulfonate (e.g. mesylate, tosylate,or triflate). Then reductive elimination is achieved by reaction withzero valent nickel or palladium to produce the polyphenol precursor. Thedeoxygenated product is then demethylated using a catalyst includingpyridinium hydrochloride or boron tribromide to give the polyphenol. Thepolyphenol is then reacted with cyanogen bromide or similar cyanogenhalide and a base including triethylamine to yield the cyanate ester.

Scheme 1. Conversion of syringaldehyde to cyanate esters by initialdehydrodeoxygenation followed by a McMurry coupling.

Scheme 2. Conversion of syringaldehyde to cyanate esters with initialdehydrodeoxygenation followed by reductive electrochemical coupling

Scheme 3. Conversion of syringaldehyde to cyanate esters without initialdehydrodeoxygenation (McMurry coupling)

Scheme 4. Conversion of syringaldehyde to cyanate esters without initialdehydrodeoxygenation (electrochemical coupling)

Embodiments of the invention generally relate to methods for makingthermosetting resins from syringaldehyde including, deoxygenatingsyringaldehyde by conversion to a sulfonate and reaction with areductive elimination catalyst to produce 3,5-dimethoxybenzaldehyde,reductively coupling the dimethoxybenzaldehyde with at least onedimethoxybenzaldehyde or at least one aromatic aldehyde having a hydroxygroup and/or methoxy group in at least one position on the aldehyde by aMcMurry reaction or by reductive chemical or electrochemical reactionsto produce at least one reductive coupling product, further reducing thereductive product(s) by hydrogenation, chemical reduction orelectrochemical reduction followed by demethylating with a hydrolyzingreagent to produce polyphenols, and converting the polyphenols with asoluble base and cyanogen halide(s) or pseudohalides to produce cyanateester resin(s).

An aspect of the invention generally relates to methods for makingthermosetting resins from syringaldehydes including, reductivelycoupling syringaldehyde with an additional molecule of syringaldehyde orat least one aromatic aldehyde having a hydroxy group, and/or methoxygroup in at least one position on the aldehyde by a McMurry reaction orby reductive chemical or electrochemical reaction to produce at leastone first reductive coupling product, further reducing the firstreductive coupling product by hydrogenation or chemical reduction orelectrochemical reduction to produce a second reductive couplingproduct, deoxygenating and demethylating the second reductive product(s)by conversion to a sulfonate followed by reaction with a reductiveelimination catalyst and further reaction with a hydrolyzing reagent toproduce polyphenols, and converting the polyphenols by reaction with asoluble base and cyanogen halide(s) or pseudohalides to produce cyanateester resin(s). Other aspects of the invention further includethermoplastics, resins, and composites produced by the methods herein.

Embodiments further include converting the polyphenols by reaction withreagents including phosgene, triphosgene, diphenylcarbonate, othercarbonates, bis(4-chlorophenyl) sulfone, other functionalized sulfones,diacid chlorides, phthalic acids, formaldehyde, other aldehydes, andepichlorohydrin to produce thermoplastics or resins selected from thegroup consisting of polysulfones, polyesters, polyester-styrenepolymers, alkylphenolics, polyarylates, polycarbonates, epoxy resins,and any combination thereof. In embodiments, the polyphenols areconverted to thermosetting resins selected from the group consisting ofcyanate ester resins, epoxy resins, benzoxazine resins, phenolic resins,bismaleimide resins, and polyether ether ketone (PEEK) resinspolyphenylene resins, phthalonitrile endcapped resins, phenylethynylendcapped resins, and other endcapped resins. In embodiments, the resinsare combined with the thermoplastics or resins and fibers or othersupport materials, and are thermally cured either with or without acatalyst to fabricate composite materials. In embodiments, thesulfonates are selected from the group consisting of mesylates,tosylates and triflates. In embodiments, the reductive eliminationcatalyst is selected from the group including zero valent nickel orpalladium catalysts. In embodiments, the McMurry reaction includescatalysts selected from the group consisting of reducible titanium(III)or titanium(IV) compounds and reducing agents selected from the groupconsisting of lithium, sodium, potassium, zinc, zinc copper couple,magnesium, magnesium-mercury amalgam, and lithium aluminum hydride. Inembodiments, the reductive coupling product produced by the McMurryreaction includes stilbenes. In embodiments, the stilbene istrans-resveratrol or cis or trans-3,3′-5,5′-stilbenetetraol.

In embodiments, the electrochemical coupling was accomplished usingelectrodes selected from the group consisting of lead, platinum,mercury, nickel, gold, and carbon and performed at a voltage at whichhydrogen evolution occurs at the chosen electrode. In embodiments, thereductive coupling product produced by the reductive chemical orreductive electrochemical reaction results in a linking group betweenaromatic rings that selected from the group consisting of vicinal diols,alkenes, ketones, alcohols, and alkanes. In embodiments, hydrogenationis achieved by using a catalyst that include a transition metal selectedfrom the group consisting of platinum, palladium, nickel, ruthenium,molybdenum, copper, and chromium and is conducted under a gas includinghydrogen atmosphere.

In embodiments, the chemical reduction is achieved by protection of thevicinal diol by functional groups subject to elimination includingacetates or oxalate, followed by reduction to a stilbene using the basewith or without a reducing metal including zinc or magnesium. Inembodiments, the electrochemical reduction is achieved by initialconversion of the vicinal diol to an oxalate, acetate, or other easilyeliminating group followed by electrochemical reduction. In embodiments,the hydrolyzing reagent is selected from the group consisting ofpyridinium hydrochloride, boron tribromide and other suitable reagents.In embodiments, the base is selected from the group consisting of alkylamines including triethylamine, alkali and alkaline earth alkoxides, andother suitable bases. In embodiments, the cyanogen halide is selectedfrom the group consisting of cyanogen bromide, cyanogen chloride,cyanogen iodide, and any combination thereof. In embodiments, thecyanogen pseudohalide is a cyanogen sulfonate, wherein the sulfonatesare defined as RSO₃ ⁻ (R=at least one alkyl or aromatic group).

PROPHETIC EXAMPLES

Any prophetic examples described herein are for illustration purposesonly and not to be used to limit any of the embodiments.

Where a range of values is provided, it is understood that eachintervening value, to the tenth of the unit of the lower limit unlessthe context clearly dictates otherwise, between the upper and lowerlimits of that range is also specifically disclosed. Each smaller rangebetween any stated value or intervening value in a stated range and anyother stated or intervening value in that stated range is encompassedwithin the invention. The upper and lower limits of these smaller rangesmay independently be included or excluded in the range, and each rangewhere either, neither or both limits are included in the smaller rangesis also encompassed within the invention, subject to any specificallyexcluded limit in the stated range. Where the stated range includes oneor both of the limits, ranges excluding either or both of those includedlimits are also included in the invention.

While the invention has been described, disclosed, illustrated and shownin various terms of certain embodiments or modifications which it haspresumed in practice, the scope of the invention is not intended to be,nor should it be deemed to be, limited thereby and such othermodifications or embodiments as may be suggested by the teachings hereinare particularly reserved especially as they fall within the breadth andscope of the claims here appended.

What is claimed is:
 1. A method for making thermosetting resins fromsyringaldehydes, comprising: reductively coupling syringaldehyde with anadditional molecule of syringaldehyde or at least one aromatic aldehydehaving a hydroxy group, and/or methoxy group in at least one position onsaid aldehyde by a McMurry reaction or by reductive chemical orelectrochemical reaction to produce at least one first reductivecoupling product; further reducing said first reductive coupling productby hydrogenation or chemical reduction or electrochemical reduction toproduce a second reductive coupling product; deoxygenating anddemethylating said second reductive product(s) by conversion to asulfonate followed by reaction with a reductive elimination catalyst andfurther reaction with a hydrolyzing reagent to produce polyphenols; andconverting said polyphenols to thermosetting resins selected from thegroup consisting of epoxy resins, benzoxazine resins, phenolic resins,bismaleimide resins, polyphenylene resins, phthalonitrile endcappedresins, phenylethynyl endcapped resins, and other endcapped resins. 2.The method according to claim 1, wherein said thermosetting resins arecombined with thermoplastics and fibers, or other support materials, andare thermally cured with or without a catalyst to fabricate compositematerials.
 3. The method according to claim 1, wherein said McMurryreaction includes catalysts selected from the group consisting ofreducible titanium(III) or titanium(IV) compounds and reducing agentsselected from the group consisting of potassium, zinc, zinc coppercouple, magnesium, magnesium-mercury amalgam, and lithium aluminumhydride.
 4. The method according to claim 1, wherein said reductivecoupling products produced by said McMurry reaction include stilbenes.5. The method according to claim 4, wherein said stilbene istrans-resveratrol or cis or trans-3,3′-5,5′-stilbenetetraol.
 6. Themethod according to claim 1, wherein said electrochemical coupling wasaccomplished by using electrodes selected from the group consisting oflead, platinum, mercury, nickel, gold, and carbon and performed at avoltage at which hydrogen evolution occurs at the chosen electrode. 7.The method according to claim 1, wherein said first reductive couplingproduct produced by said reductive chemical or reductive electrochemicalreaction results in a linking group between aromatic rings that isselected from the group consisting of vicinal diol(s), alkene(s),ketone(s), alcohol(s), and any combination thereof.
 8. The methodaccording to claim 1, wherein said hydrogenation is achieved by using acatalyst that includes a transition metal selected from the groupconsisting of platinum, palladium, nickel, ruthenium, molybdenum,copper, and chromium under a hydrogen atmosphere.
 9. The methodaccording to claim 1, wherein said chemical reduction is achieved byprotection of said vicinal diol by functional groups subject toelimination including acetates or oxalate, followed by reduction to astilbene using said base with or without a reducing metal including zincor magnesium.
 10. The method according to claim 6, wherein saidelectrochemical reduction is achieved by initial conversion of saidvicinal diol to an oxalate, acetate, or other easily eliminated groupfollowed by electrochemical reduction.
 11. The method according to claim1, wherein said sulfonates are selected from the group consisting ofmesylates, tosylates and triflates.
 12. The method according to claim 1,wherein said reductive elimination catalyst is selected from the groupincluding zero valent nickel or palladium catalysts.
 13. The methodaccording to claim 1, wherein said hydrolyzing reagent is selected froma group consisting of pyridinium hydrochloride, boron tribromide andother suitable reagents.
 14. Thermosetting resins produced by the methodof claim
 1. 15. Composites produced by the methods in claim 2.